A polyimide resin, which combines excellent heat resistance, electrical properties, mechanical properties, and the like, is widely used in surface protection films and interlayer insulating films for semiconductor devices. Generally, the polyimide resin is now often provided in the form of a photosensitive polyimide precursor composition. In the process of producing a semiconductor device, the precursor composition can be coated on a substrate such as a silicon wafer, patterned with an active light, developed, and subjected to heat imidization treatment or the like to easily form a surface protection film, an interlayer insulating film, or the like serving as a part of the semiconductor device. Thus, the process for producing a semiconductor device using the photosensitive polyimide precursor composition has a feature that it enables production steps to be significantly reduced compared to a conventional production process therefor employing a nonphotosensitive polyimide precursor composition, which requires the formation of a surface protection film or the like before patterning by lithography.
However, the photosensitive polyimide precursor composition requires the use of an organic solvent such as N-methyl-2-pyrolidone as a developing solution in the process of the development thereof. As a result, there has been a need for such a countermeasure that the organic solvent is removed in view of increased recent concern over environmental issues, and the like. In response to the need, various proposals have been made in which heat-resistance photosensitive resin materials are used which can be developed with an alkaline aqueous solution as is the case with a photoresist.
Among others, attention has been given in recent years to a method disclosed, for example, in Patent Document 1, which involves mixing an alkaline aqueous solution-soluble hydroxypolyamide becoming a heat-resistant resin after being cured, for example, a polybenzoxazole (hereinafter also referred to as “PBO”) precursor, with a photo-acid generator such as a photosensitive diazoquinone compound to make a PBO precursor composition, and using the PBO precursor composition as a positive photosensitive resin composition.
The mechanism for developing the positive photosensitive resin composition exploits that whereas the photosensitive diazoquinone compound and PBO precursor in unexposed areas have low rates of dissolution in an alkaline aqueous solution, the exposure induces the chemical change of the photosensitive diazoquinone compound into an indene carboxylic acid compound to increase the rate of dissolution of exposed areas in the alkaline aqueous solution. The difference in the rate of dissolution in a developing solution between the exposed and unexposed areas can be used to form a relief pattern consisting of the unexposed areas.
The above PBO precursor composition can be exposed and developed with an alkaline aqueous solution to form a positive relief pattern. In addition, heat produces the formation of an oxazole ring to allow a PBO film after curing to come to have heat-cured film characteristics comparable to those of a polyimide film. Thus, the PBO precursor composition has received attention as a promising alternative material for an organic solvent-developed polyimide precursor composition.
However, the PBO precursor composition has a problem that it is low in sensitivity compared to the photosensitive polyimide precursor composition; there is a need for a composition having higher sensitivity.
Patent Document 1: JP-A-63-096162